1. Field of the Invention
The invention relates to a negative-working radiation-sensitive mixture containing
a) a compound which contains at least one --CBr.sub.3 group bound to an atom not linked in turn to a hydrogen atom and which forms a strong acid on exposure to actinic radiation, PA1 b) a compound containing at least two acid-crosslinkable groups, and PA1 c) a water-insoluble polymeric binder which is soluble, or at least swellable, in aqueous alkaline solutions and contains phenolic OH groups. PA1 a) 0.2 to 10% by weight based on the total amount of b) and c) of a compound which contains at least one tribromomethane sulfonyl group, wherein the compound forms a strong acid on exposure to actinic radiation, PA1 b) a compound containing at least two acid-crosslinkable groups, and PA1 c) as a water-insoluble polymeric binder which is soluble, or at least swellable, in aqueous alkaline solutions and contains phenolic OH groups, a homopolymer or copolymer of an alkylated or nonalkylated hyroxystyrene, the homopolymer or copolymer having a removal rate of 200 to 3,000 nm/min at 21.degree. C. in an aqueous alkaline developer containing 2.38% by weight of tetramethylammonium hydroxide, PA1 A) complete stripping of the resist layer in the unexposed regions and not more than 20% reduction of the film layer thickness in the exposed regions, PA1 B) complete stripping of the resist layer in the unexposed regions and more than 20% reduction in the film layer thickness in the exposed regions, PA1 C) incomplete stripping of the resist layer in the unexposed regions. PA1 3. Determination of the cross-sectional shape of the line patterns by investigation with a scanning electron microscope. In this examination, a distinction is made between the shapes D) to G): PA1 D) orthogonal edges and an at most slightly rounded shoulder, PA1 E) undercut edges, PA1 F) trapezoidal cross section and PA1 G) trapezoidal cross section with so-called trailing edges. PA1 H) no formation of visible precipitates and deviations in sensitivity of &lt;5% compared with the sensitivity originally established after 120 days' storage at room temperature, PA1 I) visible precipitates and/or a deviation in the sensitivity of &gt;5% compared with the sensitivity originally established after 120 days' storage. PA1 K) the deviation from the mask was &lt;5%, PA1 L) the deviation from the mask was &lt;10%, PA1 M) the deviation from the mask was &gt;10%.
The invention furthermore relates to a radiationsensitive recording material which is produced therewith and which is suitable, in particular, for the production of photoresists and also for the manufacture of electronic components and printing plates or for chemical milling.
2. Description of Related Art
A plurality of lithographic techniques are currently used to produce microelectronic circuits. Using g-line lithography (436 nm), which is normally applied to conventional positive-working diazonaphthoquinone/novolak formulations, it is possible to produce resist images having a resolution of down to 0.8 .mu.m. Still finer structures (down to 0.5 .mu.m) can advantageously be imaged on a resist layer with the aid of i-line lithography (365 nm). More recent modifications of i-line lithography such as, for example, phase-shifting mask technology, make it possible to reduce the structures to be imaged further, down to about 0.4 .mu.m or less. A still higher resolution can be achieved with UV2 photoresists. In this connection, two irradiation techniques are used: the UV2 broadband exposure (approximately 240 to 260 nm) or exposure with KrF excimer lasers which emit at 248 nm.
The continuous reduction in the structures, for example, in chip production down to the region of less than 0.5 .mu.m, requires modified lithographic techniques in which even negative-working photoresists are preferably used for specific applications. To image such fine structures short-wavelength radiation is used, such as high-energy UV light, electron beam radiation and X-rays. The radiation-sensitive mixture must be matched to the shortwave radiation. A list of the requirements imposed on the radiation-sensitive mixture is quoted in the paper by C. G. Willson entitled "Organic Resist Materials--Theory and Chemistry" [Introduction to Microlithography, Theory, Materials, and Processing, edited by L. F. Thompson, C. G. Willson, M. J. Bowden, ACS Symp. Ser., 219, 87 (1983), American Chemical Society, Washington]. There has therefore been an increased requirement for novel, in particular, negative-working, radiation-sensitive mixtures which can be used in the more modern technologies such as deep UV lithography [exposure, for example, to excimer lasers at wavelengths of 248 nm (KrF), and 193 nm (ArF)], electron beam lithography or X-ray lithography.
Negative-working radiation-sensitive mixtures which contain bisazides as crosslinking agents and binders derived from isoprene are known. They are used as radiation-sensitive layers in the production of printing plates, printed circuits and integrated circuits. Their use in microlithography is, however, limited by various technical disadvantages. Thus, it is difficult to produce high-quality layers without faults (pinholes). The heat resistance of such mixtures is inadequate, i.e., the resist images are distorted by thermal flux during the processing. Finally, their resolving power is limited to structures of &gt;2 .mu.m since they exhibit undesirably high swelling during the necessary development with organic solvents even in the cured regions, and this in turn results in structural distortions or inhomogeneous development processes and, consequently, in inaccurate reproduction of the image presented through the exposure mask.
In order to be able to produce resist images having a resolution of better than 2 .mu.m, other negative-working radiation-sensitive mixtures have been developed which are sensitive to radiation of shorter wavelength, for example to high-energy UV radiation, electron beam radiation or X-rays. Such a mixture contains, for example, a copolymer of 2,3-epoxypropyl methacrylate and (2,3-dichloropropyl)methacrylate (DCOPA) or a combination of the corresponding homopolymers. However, the glass transition temperature of this mixture is too low for many applications, and, in particular, the low resistance of the mixture to plasma etching is to be criticized. In addition, this resist material also has to be processed with developers based on organic solvents with low environmental acceptability. A low resistance to plasma etching is also exhibited by other negative-working photoresists known hitherto and having a primarily aliphatic base.
EP-A 0 164 248 described an acid-curable mixture which can be developed in aqueous alkaline solutions, has an improved resistance to plasma etching as a result of the use of aromatics and is sensitive to near UV light (350 to 450 nm). In this case, the acid formers mentioned are, in particular, sulfonic acid ester derivatives of diazonaphthoquinone which form weakly acidic carboxylic acids on exposure and are therefore effective only at comparatively high concentration. As a consequence of the weak absorption and of the inadequate bleaching behavior of the photolytic acid former, such mixtures have, however, a low sensitivity to DUV radiation, electron beam radiation and X-rays.
U.S. Pat. No. 3,692,560 describes an acid-curable mixture which contains an acid-crosslinkable melamine derivative, a novolak and chlorinated benzophenones as photolytic acid formers. These mixtures do not have an adequate sensitivity in the deep UV range either. In addition, acid-curable mixtures containing photolytically formed hydrochloric acids as crosslinking catalysts often respond unusually sensitively to the smallest changes in the processing procedure, with the result that their practical use is limited.
The same applies to the acid-forming derivatives of DDT which are mentioned in EP-A 0 232 972 and which are highly toxic and for that reason alone cannot therefore be suitable for practical use. All the same, such compounds exhibit an appreciable sensitivity in the deep UV range (200 to 300 nm) and, when combined with polyhydroxystyrenes which are transparent in the UV range, yield radiation-sensitive mixtures having relatively good reproduction properties. The same patent also mentions certain aliphatically brominated cyanuric acid derivatives as photolytic acid donors. Since, however, these compounds may thermally eliminate hydrogen bromide, mixtures containing them have a limited shelf life.
Radiation-sensitive mixtures have furthermore been proposed which contain photolytic acid donors which form organic sulfonic acids on exposure. Examples are the bissulfonyl- or carbonylsulfonyldiazomethanes disclosed in the German Patent Application P 40 06 190.6, equivalent to U.S. patent application Ser. No. 07/661,823, filed Feb. 27, 1992 or the pyridones containing N-sulfonyloxy groups described in the patent applications P 41 12 967.9, P 41 12 966.0 and P 41 12 965.2, respectively, equivalent to U.S. Pat. Nos. 5,286,867; 5,229,254; and 5,230,985, each filed Apr. 20, 1992. Although practical results can also be achieved with the mixtures cited therein, there are a number of reasons why they do not make optimum image reproduction and processing possible: the bisarylsulfonyldiazomethanes mentioned in German Patent Application P 40 06 190.6 absorb relatively intensively in the deep UV2 range and do not therefore make it possible to provide resist materials which are both highly sensitive or produce orthogonal resist edges with small structures of &lt;0.35 .mu.m. The carbonylsulfonyldiazomethanes mentioned in the same documents do not yield adequate quantities of acid and the pyridones containing N-sulfonyloxy groups are relatively strong solubility inhibiters which prevent an adequate solubility gap between exposed and unexposed regions.
Further compounds which form a strong acid on irradiation with high-energy light are, in particular, onium salts, such as diazonium, phosphonium, sulfonium and iodonium salts of non-nucleophilic acids, such as HSbF.sub.6, HAsF.sub.6, or HPF.sub.6 [described in J. V. Crivello, Polym. Eng. Sci., 23 (1983) 953]. In addition, halogen compounds, in particular chromophore-substituted trichloromethyltriazine derivatives, trichloromethyloxadiazole derivatives, o-(quinone diazide)sulfonyl chlorides and o-(quinone diazide)-4-sulfonates have been recommended.
These compounds are used in negative- or positive-working radiation-sensitive mixtures. The use of such photolytic acid formers entails, however, disadvantages which drastically restrict their possible uses in various fields of application. For example, many of the onium salts are toxic. Their solubility in many solvents is inadequate, and for this reason only a few solvents are suitable for producing a coating solution. In addition, when onium salts are used impurity atoms, some of which are undesirable, are introduced and these may result in process disturbances. This is a particular problem in microlithography. Furthermore, the onium salts form very highly corrosive Br.phi.nsted acids during photolysis. These acids attack sensitive substrates, with the result that the use of such mixtures leads to unsatisfactory results. The chlorine compounds and the quinonediazidesulfonylchlorides form hydrochloric acids, with the above-mentioned disadvantages. In addition, on certain substrates such compounds have only a limited durability. The durability has been improved by inserting an interlayer between substrate and radiation-sensitive layer, but this resulted in an undesirable increase in defects and in reduced reproducibility (See DE-A 36 21 376, equivalent to U.S. Pat. No. 4,840,867).
More recent work by F. M. Houlihan et al., SPIE 920: 67 (1988) showed on the basis of positive-working systems that, in addition to the above-mentioned acid formers, nitrobenzyl sulfonates, which form sulfonic acids having low migration tendency on exposure, can also be used in certain acid-labile resist formulations. From these results it can be deduced that such compounds can also be used for photocurable systems.
Despite the intensive research activity carried out hitherto in this area, no radiation-sensitive mixture is currently known which does not have the problems and disadvantages described above and with which a negative-working radiation-sensitive recording material can be produced which is capable of combining the advantageous properties described at the outset with one another.